For miniaturization of semiconductor devices, the trench gate structure with the gate electrode formed in the trench is adopted. In the trench gate structure, the current channel is formed in the vertical direction perpendicular to the substrate. Thus, the lateral gate spacing can be narrowed. Accordingly, the device structure can be miniaturized, and the effective channel width can be widened. This makes on-resistance lower than in the gate structure in which the channel is formed in the lateral direction. Furthermore, because the device size is reduced, the trench gate structure is also advantageous in increasing the switching rate to achieve higher performance.
In such a semiconductor device, compatibility between lower on-resistance and higher breakdown voltage is important.